Crystalline Tin Disulfide by Low-Temperature Plasma-Enhanced Atomic Layer Deposition as an Electrode Material for Li-Ion Batteries and CO₂ Electroreduction

Tin disulfide (SnS2) is a promising candidate for electrochemical applications, showcasing improved performance via tailored structure and morphology. This study discusses a plasma-enhanced atomic layer deposition (PE-ALD) method for depositing crystalline SnS2 thin films using the tetrakis(dimethylamino)tin(IV) precursor and H2S plasma at temperatures of 80 and 180 degrees C. X-ray diffraction confirms a layered hexagonal crystal structure and strong c-axis-oriented film growth, with the alignment of the basal planes mainly parallel to the substrate. At 80 degrees C, the film surface consists of continuous grain-like structures, whereas at 180 degrees C, the smooth film surface during the initial growth evolves to out-of-plane oriented structures when more SnS2 is deposited. The influence of crystallinity and surface morphology on the electrochemical performance of crystalline SnS2 thin films deposited by the PE-ALD process is evaluated for Li-ion battery and electrochemical CO2 reduction applications. A comparison is made with those of amorphous SnS2 thin films deposited by the corresponding thermal ALD process. As an anode material in Li-ion batteries, the SnS2 thin film with out-of-plane oriented structures outperforms the other films with 77% capacity retention after 100 charge/discharge cycles despite its lower initial capacity. In contrast, the crystalline SnS2 with grain-like morphology and amorphous SnS2 retain only 65 and 34%, respectively, of the initial capacity after 100 charge/discharge cycles regardless of their higher initial capacity. In a similar fashion, the SnS2 thin films with out-of-plane oriented structures exhibit lower Faradaic efficiencies for formate production by CO2 electroreduction at 100 mA cm(-2) as compared to SnS2 with grains (i.e., 64 vs 80%) albeit at lower overpotentials (i.e., 260 mV less negative) and maintaining a better structural and electrochemical stability. The amorphous SnS2 thin film showed similar Faradaic efficiencies (i.e., 80%), stability, and overpotentials (i.e., -0.84 V vs RHE) compared to the crystalline SnS2 thin film with a grain-like morphology.